Kumbh Mela, the world's largest religious festival

The world's biggest gathering of humanity, the Kumbh Mela pilgrimage, is underway in Allahabad in India. It’s expected to draw millions, a lively and colourful affair, with Hindu religious men arriving by elephant-drawn carriages and scores of people ritually washing where three rivers meet. But the festival is a logistical challenge, with health and safety worries hanging overhead.